From DE 33 01 071 C2 a device is known for lowering and raising a window pane of a motor vehicle which comprises a switch-on member which becomes active when the door is opened and closed and whose signal is evaluated by a control device. Depending on the voltage which momentarily arises, one of two proposed time switch stages will respond whereby the drive motor is set in motion in the controlled direction for a designated time period dependent on the voltage interval.
The device described serves to lower the upper edge of the window pane from a positive sealing engagement of a sealing element on the body work side. The lowering of the window pane, triggered by the unlocking of the vehicle door, is thereby carried out just so far that the door can be opened without problem. On the other hand through changed conditions, such as increasing the system deficiency of the adjustment device and reducing the operating voltage, there is the danger that the upper edge of the window does not completely leave the sealing area. It is therefore usual up until now to control the drive for a period of time in the lowering direction, which contains an additional time reserve and in each case is adequate for a sufficient lowering of the window pane.
A disadvantage of the prior art is that the requirements for anti-jam protection, more particularly US requirement FMVSS 118 .sctn. S 5, can no longer be observed if through the motorized lowering of the window pane there is still a gap existing which exceeds the maximum width of 4 mm. For as a result of the system elasticity and the reverse play of the window lifting mechanism, a person resting on the top edge of the window pane or vibrations can lead to the window lowering further by several millimeters. In these cases the use of a comparatively expensive anti-jam protection would be required in order to obtain an operating permit.
One possibility of avoiding the short stroke lowering of a free-standing frameless window pane lies in using a pure force locking connection between the seal and the edge of the window. However this has the drawback that a high structural expense has to be incurred for guiding and adjusting the window. The large friction forces which are necessary between the edge of the window and the seal create very high closing forces. Furthermore restrictions regarding the aerodynamics in this area have to be taken into account, which causes increased wind noises.
From EP 0 270 837 A1, a method is known for regulating the position of moving parts of NC and CNC machine tools wherein after reaching the ideal position of a component part of the machine tool a reversal signal is produced which changes the direction of rotation of the drive motor. The normal position regulation is stopped and a predetermined resetting value produced which turns the drive motor back by an angle corresponding to the reversal span. This method cannot however be transferred to controlling a window pane in a motor vehicle. For here it is not a question of compensating a predetermined reversal play which is produced through the play of individual gear elements, but it is rather a matter of compensating a system deficiency which can change through extraneous force action and ageing, and is therefore variable.